Here's a thought if your in an area you can't find any decent trellis netting to buy. Go buy yourself some pvc pipe. The size is dependent on you and how rigid you would like it to be. In any case you can use 1/2 to 1 1/2 i would suspect being way bigger than anything anybody would need.
Take the pvc and depending on what size squares you want drill holes straight through the pvc in set increments. Then cut the pvc to length depending on your screen size again. Remembering to center cuts so that its equal on the ends so its easier on yourself. Connect your frame and weave your desired wire, rope, twine, or w/e you can think of to use and there you go custom sized scrog net.